Method of blowing iron



Feb. 5, 1952 F. L. MORRISON 2,584,152

METHOD OF BLOWING IRON Filed July 2, 1951 INVENTOR. FLOYD L. MORRISON.

ATTORN EY- Patented Feb. 5, 1952 "Floy'd' L. 'Morrison, Trenton, .Mieln, 'ass'ignor to National Steel Corporation, a corporation-of Delaware Application-July}, 1951,.SerialNo.{234,855

' '21 Claims.

"This invention relates to. improvements in blowing. .blast furnace iron in a .converter and more particularly relates to improvements in the operation of such. aconverter for effecting improved separation of the slag from the molten metal to produce cleaner 'blown metal and for effecting other advantageous results. IThisapplication is. a continuation-impart of mylcopending application'seria'l No; 785,2l8'ffiled November'1'2, 1947, entitled Methodof'Blowing Iron}"'now abandoned.

1 "Insteel plants utilizing the Bessemer process, molten .pig. iron from the blast furnace'is charged into an acid type converter and the charge thenblown with an airblast. 'The blowing operationreduces .the silicon, manganese and carbon content 'ofithe molten metal ithrough oxidation reactions and produces moltenlslag containing these constituents in addition to iron oxide. "The blown metal, which (is 'molten Bessemer imetal,

maybe formed'directly into Bessemersteel products or maybe used in the usual duplex process to produce difierent typesio'f'steel. "The metalin theiconverterat the. end of the blow "will contain 015% carbon, or less. .In order to produce'iron which canbe successfully 'blown .in the Bessemer converter,".the'materials charged toi'theblast "furnace 'are'so proportioned; and the blast furnace is so operated as to produce molten blast furnace metalcontaining'up 1 to'about .5% to 37% manganese 'andfcontainin'g about 1.25 to 1.8 sili: 'con' w'iththe ratioof silicon to'manganese not l'essith'an '2 and preferably about 2.5 or higher. Preferably, both the silicon and the ratio of silicon to manganese are maintained .on. the high side, and the manganese is maintained 'on-the low side; "The manganese; upon oxidation, forms a relatively fluidslag," and a high'manganese content may produce aslagso fluid that slapping-will joccur during the blow and "so fluid "that the slag will not separate cleanly from the metal. Oxidation "of the silicon during the-blowing operation :is an important source'of heat so that, if thesilicon is -too;lw,"-a cold blow willresult. "Further, if the siliconis low, there is a*tendency to form a corrosive slagbecause*of"the"-relatively 'higher iron oxide'content'of the slag.- Accordingly'when blowingmolten iron inthaconverter to produce Bessemer steel, itis necessarythat the molten iron contain a relatively high ratio of silicon'to manganese. At least at'times, and despite the fact that the molten .iron contains the properratloof siliconto manganesaithe slag ma ner .separate .as-clearilyas desired. k v me steel Pieer rs? 1- p e um tion of .the'blast furnace iron is'charged directly to thebasic openhearth furnace to'produ'c'e open hearth steel, the blast furnace is operated to produce iron containing quite diiferent amounts of manganese and silicon. In orderto produce good iron forthe Open hearth; theicharge 'to"the blast 'furnace is so proportioned as to produce iron containingiabout 1.25% to "1.75% manganese with about manganese being preferable. Thesilicon content of the iron is :about .8 to 12 with "about 1 'beingpreferab'le. The 'silicon tom'anganese ratio is maintained relatively low and "preferably "is "less than about 1. The relatively high per cent of "manganese-reduces the amount of ferromanganese which must be addedto the -open hearth steel'in the ladle "and increases the fluidity of the slag which reduces the timerequired to'workthe heat. A relatively long'period is required to work a heat'inan open hearth furnace, and it is particularly desirable that this period be reduced as much-as possible.- The amount of silicon "is maintained relatively low to'reduce the-attack on the basic lining "of'the open hearth furnace and to reducethe amount of limethat mustbebhargedinto thefurnace.

'Scme steel plants utilize -the Weirton process described inPatentNo'. 2,390,346, which is'anacid converter-basic openi hearth process, 'to augment their production of open hearth steel. In such plants, some 'ofjthe blast furnace iron is charged to'ithe converter, but most of 'theiron'is charged to the .open hearth furnace. The molten jpig'liron usually .is periodically withdrawn from the blast furnaceand placed .ina relatively-large mixer to supply the pig iron for the converter as well as the ,pig iron for .thelopen hearth. The blast furnaceis operated to .produce .an iron that is, or is more nearly, satisfactory for'the open hearth furnace thanforthe converter as the plant is primarily interested in producing open Ihearth steeLand .theconvertenmerelyincreases.the output of steel per open hearth furnace. Quite. often, only a relatively small percentage .of iron is blown in the converter. Such .an iron may con tain, for. example, about .9%' to1l.3% manganese and .from about -.9 %v to 1.25% vsilicon, and the silicon :to manganese .ratio is preferably Iabout onenor'less. ..At times ,f.the silicon to ,manganese ratio may besomewhat higher but is less than 1.5 and is less-than the-minimumusually considered desirable forgood converter operation. This iron cannot be satisfactorily, completeli blown .in theconverter to produceBessemensteeh. JntheWeirton process, :the, ironlis.,not blown all .the way .down and. =the.blow,-.is stopped before the carbon content is reduced to 1% and preferably the carbon content is reduced to between 2.5 to 1 One serious difficulty encountered when blowing such an iron in the converter is that as a result of the relatively high manganese content and the relatively low ratio of silicon to manganese, the fluidity of the slag tends to be excessive so that slopping may occur and the slag does not separate cleanly from the blown molten metal. The presence of slag in the blown metal from the converter is highly undesirable, especially as the blown metal is charged to the open hearth furnace. One important difficulty caused by having slag in the metal charged'to the open hearth is that as the slag is acid, the lining of the open hearth furnace is attacked and the amount of lime charged must be greatly increased. Another difilculty resulting from slag in the blown metal is that the steel from the open hearth furnace and the products produced therefrom tend to contain a relatively larger quantity of slag inclusions which are undesirable.

Accordingly, a primary object of this invention is to efiect improved separation of the slag from the metal in the converter. Y

Another object of the present invention isto provide an improved process of operating a converter that will effect better separation of the slag from the metal.

Another object of .the present invention is to provide an improved process of operating a converter that will effect better separation of the slag from the metal when the blast furnace metal charged to the converter contains silicon and manganese in a relatively low ratio of not more than 1 I A further object of the present invention is to effect improved separation of the slag from the metal in the converter when the blast furnace metal charged to the converter contains silicon and manganese in such quantities that the blast furnace iron is suitablefor charging into an open hearth furnace and contains from 0.9% to 1.3% manganese and from 0.9% to 1.25% silicon.

It ,is also an object of the present invention to effect improved separation of the slag from the metal in the converter when the'blast furnace metal contains a relatively low ratio of silicon to manganese without causing excess fluidity of the slag which would result in slopping and incomplete separation of the slag from the blown metal.

Another object of the present invention is to provide an improved process of operating a converter that will increase the life of the converter lining, particularly the bottom.

It has been discovered that enriching the converter blast with oxygen during the final or finishing period of the blowing operation improves the clean-up or separation of the slag from the metal so that the blown metal poured from the converter is cleaner and is relatively free of undesirable slag inclusions. The improvement in clean-up of the metal is, of course, more pronounced when the charge of blast furnace iron contains silicon and manganese in a ratio of less than 1 for normally it is difficult to' have the slag separate cleanly from the metal under such conditions. In the Weirton process, the silicon to manganese ratio is about 1 and preferably less, and increasing the oxygen content of the blast during the finishing period is especially helpful as obtaining good slag separation is quite difficult and important. Although the present invention is more particularly useful in obtaining sepa ration when the silicon to manganese ratio is less than 1 and especially so when this ratio is 1, or less, the present invention is not limited to such ratios and is useful for obtaining more complete slag separation when the silcon to manganese ratio is higher than 2 and the metal is not blown down to less than 0.25% carbon. At least, at times, it is difiicult to obtain complete or satisfactory separation of the slag when the blast furnace metal is of the type usually considered satisfactory for producing Bessemer steel. It also has been found that the use of an oxygen en- 'riched blast during the clean-up period to improve the slag separation does not cause excessive fluidity of the slag and slopping during the blowing operation. This is somewhat surprising for heretofore the primary reason for suggesting the use of an oxygen rich blast in the converter has been based on the fact that more heat would be available and excess heat may cause excessive fluidity which will cause incomplete separation of the slag and slopping during the blow.

An important advantage of the present invention is that cleaner blown metal is produced. Another important advantage is that the blast furnace can be operated to produce blast furnace iron that is suitable for charging to the open hearth furnace as is done in the Weirton process, and such a blast furnace iron can be charged to the converter and readily blown to produce clean blown'metal without taking unusual precautions; Consequently, the blast furnace can be operated to produce good iron for the open hearth without altering the blast furnace process when some of the pig. iron is to be charged to the converter and blown.v

vIt is the oxygencontent of the blast during the final or finishing period of the blowing operation that effects the separation of the slag. The length of the finishing period will depend in part upon the pressure of the blast, the quan: tity of the blast in cubic feet per minute and the percentage of oxygen in the blast. The finishing or clean-up period may constitute, up to the last 1 to 2 minutes of the blowing period preceding discharge of the blown metal, Nor-,- mally, the finishing .periodwill be at least A minute, but this depends in part on the oxygen content of the blast and will be discussed more fully in connection with the oxygen content of the blast. Preferably, the finishing period is maintained as short asis consistent with 'good slag separation, so that preferably the finishing period is not longer than 1 minutes. Good results can be obtained with a finishing period of from A to minute.

If the percentage oxygen content of the blast during the finishing period is greater than that of air, improved slag separation results. Economic factors at the present time tend to limit the percentage oxygen content. In addition, it is-desirable that the finishing period not proceed too rapidly so that normally the blast during the finishing period does not contain more than 30% by volume of oxygen and preferably does not contain more than 25% oxygen.

These and other objects and advantages will become more apparent when considering the following description, taken inconnection with the accompanying drawing in which there is a diagrammatically shown apparatus including an acid type converter constructed and arranged for carrying out the present invention.

Referringto the drawing, an acid-type, re fractory lined converter I0 is pivotally or tiltably mounted on a pair of trunnions H and I2 rotateases-mus ably-supported in a pair of supports [3; Atithe: bottom of the converterg -therei is av windibox. l 4 which is in communicationwith the outletend of apipe P5. The outlet side of ablower 161 is. connected through pipe I], hollow? trunnion l2 and pipe'lt'tothe-windbox [4. .A pluralityof tuyres F8 are in communication". withiwind' box:

M sc that whenthe blower I6? is inoperatiom. a

blast of air is blown through the tuyres l81and. the' moltenmetal in the converter ID.

i Means are "provided" for: increasing theioxygen; content of the blast; A. tank l9 which may-abs; arelatively large storage-tank or which may be% connected through alpine-W to a. source. of pure. or impure-,oxygen is: connected through pipe; 2| to pipe I'T. Pipe 2!; contains afiow control valve: 2 2' "-which maybe opened to admitthe: desired. amountof oxygen. to. pipe l1. added 'to pipe H, the; oxygen. pressure. must be higher than the blastrpressure. on the outlet: side. of blower' l 6 so. that the oxygen will. flow into the pipe Hand mix with the; air blast. Preferably, the oxygen is added to .the inlet: side of the blower; Pipe 23containing-valve24 is connected tooxygen pipe 2| and. to an inlet pipe 25.0f blower. i5. Inlet pipe is. connected to a suitableisourcebf blast air which; may be atmospheric; air. With valve, 24 open, oxygen flows. through pipe. 23, pipe 25 and, the blower; It. When. the. oxygen is: added to the blast on the inlet sideof the blower, the. pressureof the. oxygen can be relatively low.v The oxygen may be pure. oxygen. or' impure: oxygen if it, is of sufiicient. purity so: that it can be used. to enrich. the; air blast.

i In operation, the; converter i0 is turned downto substantially thehorizontal position and is; chargedwithmolten blastfurnace. iron. As soon as. the converter is charged, the: blowerl6 isv started and the. blast isiturned' on, and" simul-; taneously the converter; is turnedv to the. erect position. The blast of .air' flowsup through the molten iron and scrap, if any, to oxidize the carbon, silicon, andmanganese. During the first part' of the blowing operation, the silicon is rela-.- tively: rapidly oxidized,. and. only: a. small amount of 'the carbon isoxidizedp. During the interme: diate blowing step, both the silicon and carbon. are-oxidized in more nearly equal amounts. During thefinishing or final period immediately'preceding: discharge of the blown, metal, only a. slight amount. of? silicon is oxidized while a: relatively-large amount of carbon is oxidized. The oxidized silicon and manganese, along with the oxidized iron,.. form asslag. which floats on top of themolten metal. If conditions are such that thes'lag separates. cleanly from the. metal, only a slight amount of slag or no slag will be left in the molten. metal.

. As. more: fully" described inmy copending ap- When. oxygen is:

plication; Serial No. 785,219,:filed. the same. day

as the parent application, Serial No, 785,218,.n0w abandonechtheuse ofan oxygen rich blast during-the first portionormelt-down periodof the blowing. operation increases. the: amount of scrap which can be chargedandreduces, theblowing. period. If oxygen enriched-blast is used during the melt-down period, the silicon content of the metal is-reduced to a lower value than when the usual air blast is used. This increases, at least to a slight extent, the amount of slag, and if an oxygen enriched blast is used during the finishing period, this increased quantity; ofvslag will separate cleanly from. the blown metaL,

1 AZnumberof blowstweres'made. inwhich about.

8;000; to 11,000 pounds-.uofrsollde 8, 13 131 steeleand; from about 45,000 to t.47,0.0.0% :poundsi. of; molten;

blast; furnace iron were charged; into the; converter for each.blow-.: '.Theseechargeswerezblown. with .a, blast of atmospheric; air: containingv the normali quantityi of moisture present; in the; airand'. enriched .with-isu'iiicient: oxygen during the period: set: forth. so as to. contain. the: percentageof oxygen. specified. which is...the: tQtaIpercentaEQ of-oxygen. The blast: furnaceiron; contained from. 4'.0..to 4.40%,= carbon, from .90. te l-.3091.

manganese, and" from.-.9J to 1.25%,si1icon, The. blast pressure: was abouttz5' pounds 'persquare.

inch, and .the 'blastuvolume: was: about: "3 ,000- cubicfeeu er: minute, .A. number: of .b10WSTWeI6-..

made with: theiblast: during the finishingperiod containingabout 24%;. to 25%: volume of'oxygen Fora. few blows; the blast; contained about 22.5%- oxygen; This finishing. period was varied in. length from- 3/4 .to. 2:1minutes.. For'somezoffthe .blowsvand in addition. to enriching; theblast,

when the scrap was: melted. or was: discontinued; I before the; scrap. was melted andthersilicorrcon.

tent of the; blown metal. was.v on theaverage, less than iorxthe;v other blows; The; bIaSt eXceptfor the periods of: enrichment, was atmospheric-Fair. In all of these examples, the carbon wasreducedl to from 1.44Jt0: 2.43%. Immediately after the finishing period, theconverter was; turned down,

the. blastdiscontinued; and; the blown metal and slag discharged fromv the.-converter. Whenvthe; blown metal-uwaspoured, the slag separated cleanly from the metal. and. separated; more cleanly than when; similarblast furnace,iron-- was: blownwithastraight. air blast. The blown metal. was relatively free of; slag inclusions and wassuccessfully charged, and worked in; the operr hearth; furnace.

In another: series of,. blows. with: similar blast.

furnace. iron, the. blast; pressure. wasabout. 2.6

poundaper square. inch, andtheblast volume The.

tained on the: averageabout:22,;65;%.v total ox gen;

by volume. 'Theblast. preferably should "not contain. more than about 2.5% oxygenas-vthere isa tendency: for: the; finishin'gtperiod to proceed so rapidly that. it-. is.1difficult:to control and pref.- erably should contain! at leastzabout 2-1 .5 oxygen; by volume so asznot to. lengthen the finishing;

period" unduly. 1 For .somesof 1 the; blows; steam was add'ed -to the blast during various: portions.

of 1 the blowing" operation, including? thezxfinishing period sand: the. intermediate periodgbetween the melt-down and finishing periods; Theslight.

variation in the blast resulting from the; steam. 4

addition was: ignored, and the same? volume; of. oxygen-thaws; 800: cubic .feet: per: minute'e-was added to the blast. As". used herein, the. term air-blastcovers 'an airblast which may. or may not: contain: added moisture: but: which contains: 1 no added. oxygemandth'e term oxygen-enriched; air blastirdsi directedto such air. blast which" con:--

tainsc addedt.gaseousa-oxygem-aither; pure: or. 1m:

pure-so that the blast contains a higher per centage of oxygen than air.

Whileit is customary and correct to refer to the fact that during the first part of the blow silicon is oxidized or reduced and that during the last part of the blow the carbon is oxidized. eachof these elements is oxidized to a limited extent during all portions of the blow so that enriching the blast does aid in oxidizing these elements. Enriching the blast during the cleanup period may shorten the blowing period, but this eifect, if any, is very slight and is not sufficient to warrant the cost of the oxygen and has not been sufilcient to be noticeable. The use of an oxygen-rich blast during the finishing period more acute when the silicon to manganese ratio is less than 2, and especially so when such ratio is 1.5 or 1, or less. Furthermore, steam or water does have a marked effect on the slag separation. For example, in blows like those previously described, except that the, blast was not enriched during the finishing period, the white hot blown metal when poured had a dirty anpearance and black streaks of watery-appearing slag could be seen in the metal. The use of oxy gen during the first part of the blow did not reduce'the occurrence. of these slag streaks. When the blast was enriched at the end of the blow, the white hot blown metal had a clean bluewhite appearance without the streaks of slag. The additional oxygen'seemed to dry up the slag so that it separated cleanly. Regardless of whether or not this is the correct explanation, the character of the slag was changed so that it separated cleanly, and this characteristic was retained when a number of blows were poured into a ladle, prior to pouring the metal into the open'hearth. While the ladle contained some slag, the slag remained separate and did not reenter the metal. In addition, there were strong indications that products made from the openhearth steel contained on the average fewer slaginclusions when the blast was enriched with oxygen during the finishing period.

Surprisingly, it has been found the blast with oxygen increases the life of the converter bottoms. Accordingly, it is preferable to also use an oxygen rich blast during at least part of the melting period in addition to the finishing period. It has been possible to increase the average number of blows per bottom by as much as fifty per cent, and in some instances a bottom has been used for more than twice the usual number of blows where the bottom was well constructed and oxygen was used both during" the melt-down and finishing periods. The life of a" converter bottom is influenced by other factors, and is particularly influenced by the skill used in making the bottom so that it is necessary to make a comparison over an extended period, and it is difiicult, if not impossible, to express the increase in bottom life resulting from the use of oxygen enrichment in exact percentages. A long series of blows using oxygen enrichment has resulted in a great increase in the average life of the converter bottom, and this increase in average life has been about 50%.

Although the present invention has been described more particularly for use when the hot metal contains silicon and manganese-in a ratio of less than 1 /2 and in a ratio of about one, or less-for it is under these conditions that it is very difiicult to obtain complete separation of the slag from the blown metal- -the present invention is not limited tosuch blast furnace metal and may be used with blastfurnace iron containing silicon and manganese in a ratio greater than two. The-problem of slag separation i8 that enriching vapor may be added to the blast when the blast is or is not being enriched with oxygen. In addition, the blast may be enriched with oxygen in accordance with the present invention when the converter is either an acid or basic type converter.

Enrichment of the blast during the intermediate blowing period immediately preceding the finishing period produces no particular advantages and is undesirable. The use of an oxygen rich blast during this intermediate period changes the characteristics of the flame so that the operator cannot accurately control the blow,- ing operations and also increases the temperature of the metal. If the temperature of metal is increased, the carbon may be oxidized and the siliconm not properly oxidized so that the blown metal will contain a relatively large amount of silicon which is undesirable, especially when the blown metal is charged to the open hearth furnace. Accordingly, an oxygen rich blast should not be used during the intermediate period between the first or melt-down period and the finishing or clean-up period as it does not produce any appreciable results and increases the cost.

The use of an oxygen rich blast during part of the blowing period, and especially during the finishing period at the end of the blowing period, has a further advantage. Heretofore, when blast furnace iron was blown in a Bessemer converter to produce Bessemer metal, it has been considered necessary to charge the blast furnace with Bessemer, low manganese types of ores. With the present invention, it is possible to utilize the basic, high manganese ores to replace, at least in part, the Bessemer ores and obtain blast furnace iron that contains a relatively higher amount of manganese and that can be blown to produce clean blown metal.

I claim:

1. In the method of blowing ferrous metal in a converter, the steps comprising charging molten blast furnace iron containing carbon, silicon and manganese into the converter, first blowing the charge and oxidizing constituents of the iron, blowing the charge with an air blast, and then finish blowing the charge with an oxygen-enriched air blast for a period of not longer than two minutes and at least oxidizing carbon, the blown metal at the end of the blow containing at least 0.25% carbon.

' 2. The method of blowing ferrous metal in the converter as claimed in claim 1 in which the oxygen-enriched air blast contains at least 21.5% oxygen by volume.

3. The method of blowing ferrous metal in the converter as claimed in claim 1 in which the finish blowing period is at least minute and not more than 1% minutes.

4'. The method of blowing ferrous metal in the converter as claimed in claim 1 in which the ratio of silicon to manganese in the molten blast furnace iron is not greater than 1 /2.

' 5. In. the method of blowing ferrous metal in a converter, the steps comprising charging into the converter molten blast furnace iron containing carbon and containing silicon and manganese in a ratio not'greater than 1%, first blowing the charge and oxidizing constituents of the iron, blowing the charge with an air blast, and then finish blowing the charge with an oxygen-enriched air blast containing at least 21.5% oxygen by volume for a period of at least minute and not longer than 1% minutes and oxidizing carbon, the blown metal at the end of the blow containing at least 0.25% carbon.

6. The method of blowing ferrous metal in the converter as claimed in claim in which the finish blowing period is not longer than minute.

7. The method of blowing ferrous meta1 in the converter as claimed in claim 5 in which the oxygen-enriched air blast contains not more than 25 oxygen by volume.

8. The method of blowing ferrous metal in the converter as claimed in claim 5 in which the blown metal at the end of the blow contains at least 1% carbon.

9. The method of blowing ferrous metal in the converter as claimed. in claim 8 in which the finish blowing period is not longer than minute.

10. The method of blowing ferrous metal in the converter as claimed in claim 8 in which the finish blowin period is about minute.

11. The method of blowing ferrous metal in the converter as claimed in claim 8 in which the silicon to manganese ratio is about 1.

12. The method of blowing ferrous metal in the converter as claimed in claim 11 in which the finish blowing period is not longer than minute.

13. The method of blowing ferrous metal in the converter as claimed in claim 11 in which the finish blowing period is about minute.

14. In the method of blowing ferrous metal in a converter, the steps comprising charging into the converter molten blast furnace iron containing carbon and containing silicon and manganese in a ratio of about 1, first blowing the charge and oxidizing constituents of the iron, blowing the charge with an air blast, and then finish blowing the charge with an oxygen-enriched air blast containing between 21.5 and 25% oxygen by volume for a period of from M; to minute and oxidizing carbon, the blown metal at the end of the blow containing at leastl carbon.

15. The method of blowing ferrous metal in a converter as claimed in claim 14 in which the finish blowing period is about /2 minute.

16. In the method of blowing ferrous metal in a converter, the steps comprising charging solid ferrous metal and molten blast furnace iron into the converter, first blowing the charge with an oxygen-enriched air blast for a period not longer than required to melt the solid ferrous metal, blowing the charge with an air blast, and then finish blowing the charge with an oxygenenriched air blast for a period of not longer than 2 minutes, the blown metal at the end of the blow containing at least 0.25% carbon.

1'7. In the method of blowing ferrous metal in a converter, the steps comprising charging solid ferrous metal and molten blast furnace iron into the converter, the molten blast furnace iron containing carbon and containing silicon and manganese in a ratio not greater than 1 first blowing the charge with an oxygen-enriched air blast for a period not longer than required to melt the solid ferrous metal, blowing the charge with an air blast, and then finish blowing the charge with ii) an oxygen-enriched air blast containing at least 21.5% oxygen by volume for a period of at least )4; minute and not longer than 1 minutes, the blown metal at the end of the blow containing at least 0.25% carbon.

18. The method of blowing ferrous metal in a converter as claimed in claim 17 in which the blown metal at the end of the blow contains at least 1% carbon.

19. In the method of blowing ferrous metal in a converter, the steps comprising charging solid ferrous metal and molten blast furnace iron into the converter, the molten blast furnace iron containing carbon and containing silicon and manganese in a ratio of about 1, first blowing the charge with an oxygen-enriched air blast for a period not longer than is required to melt solid ferrous metal scrap, blowing the charge with an air blast, and then finish blowing the charge with an oxygen-enriched air blast containing at least 21.5% oxygen for a period of at least minute and not longer than 1 minutes and oxidizing carbon, the blown metal at the end of the blow containing at least 0.25% carbon.

20. In the method of blowing ferrous metal in a converter, the steps comprising charging solid ferrous metal and molten blast furnace iron into a converter, the molten blast furnace iron containing carbon and containing silicon and manganese in a ratio of about 1, first blowing the charge with an oxygen-enriched air blast for a period not longer than is required to melt the solid ferrous metal, blowing the charge with an air blast, and then finish blowing the charge with an oxygen-enriched air blast containing between 21.5% and 25% oxygen by volume for a period of at least A, minute and not longer than minute and oxidizing carbon, the blown metal at the end of the blow containing at least 1% carbon.

21. The method of blowing ferrous metal in a converter as claimed in claim 20 in which the finish blowing period is about minute.

FLOYD L. MORRISON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Transactions of the American Institute of Mining and Metallurgical Engineers, volume 116, 1935, pages 144 and 145. 

5. IN THE METHOD OF BLOWING METAL IN A CONVERTER, THE STEPS COMPRISING CHARGING INTO THE CONVERTER MOLTEN BLAST FURNACE IRON CONTAINING CARBON AND CONTAINING SILICON AND MANAGESE IN A RATIO NOT GREATER THAN 1 1/2, FIRST BLOWING THE CHARGE AND OXIDIZING CONSTITUENTS OF THE IRON, BLOWING THE CHARGE WITH AN AIR BLAST, AND THEN FINISH BLOWING THE CHARGE WITH AN OXYGEN-ENRICHED AIR BLAST CONTAINING AT LEAST 21.5% OXYGEN BY VOLUME FOR A PERIOD OF AT LEAST 1/4 MINUTE AND NOT LONGER THAN 1 1/2 MINUTES AND OXIDIZING CARBON, THE BLOWN METAL AT THE END OF THE BLOW CONTAINING AT LEAST 0.25% CARBON. 